1. Field of the Invention
The present invention relates to hot melt ink for an ink jet printing in which a melted ink is jetted out to form an image on a printing medium, and to an ink jet printing apparatus in which melted ink is jetted out to form an image.
2. Description of the Related Art
An ink jet printing apparatus, in which ink is jetted out to a printing medium and is fixed on the medium to form the desired image, is known. There are some types of ink applicable to the ink jet printing apparatus distinguished each other from the viewpoint of fixing mechanism. For example, there are a liquid-type-ink and a hot melt ink (solid-type-ink). The liquid-type-ink includes a solvent and is fixed on the printing medium with the solvent being evaporated. On the other hand, the hot melt ink includes a thermoplastic composition, such as a thermoplastic resin, which is used as a binder. The hot melt ink melted by heating is jetted out to the printing medium and fixed thereon by cooling.
In the liquid-type-ink, it is difficult to use pigment as coloring material, therefore, dye is forced to be used. However, the trouble is that dye is inferior to pigment in a weatherproof property. On the other hand, in the hot melt ink, since pigment can be dispersed into the binder of the ink, both pigment and dye are advantageously able to be chosen. Therefore, a good weatherproof property can be given to the hot melt ink by using pigment, if necessary.
However, the hot melt ink is usually inferior in flow property on the printing medium after the ink-jetting process, and is apt to be fixed so as to hold its shape after this process. If the ink is fixed only by cooling process after the ink-jetting process, the good fixing condition of the ink can not be gotten and some trouble, such as a deterioration in a coloring property of the image, is caused. Consequently, an additional process such as a process for heating or pressing the printing medium after the ink-jetting process is necessary to fix the ink in good condition. However, an adoption of the additional process unfortunately makes a size of the printing apparatus larger or makes the structure of the apparatus more complicated.
And furthermore, the hot melt ink mainly includes a hot melt composition, molecular weight thereof is comparatively low. Accordingly, the fixed ink is soft and it""s wear resistance is not good, therefore, there is a possibility that a set-off, that is a phenomena that an ink on a sheet is transferred to the next sheet, is caused when the sheets on which printing images are formed are piled each other.
It is an object of the present invention to provide a hot melt ink which has a good fixing property.
According to a first aspect of the invention, a hot melt ink which is applicable to an ink jet printing system where the hot melt ink is jetted out to a printing medium to form an image on the printing medium includes: a binder which contains a hot melt composition; a coloring material which is dispersed in the binder; and a photo-curing composition, wherein the binder as a dispersion medium is dispersed in the photo-curing composition in the form of grains and a surface of the hot melt ink is covered with the photo-curing composition when the hot melt ink is fixed on the printing medium.
By the above invention, a flow property of the ink which has jetted out on the printing medium is improved. Accordingly, any fixing process such as process in which heat or pressure is given to the printing medium is not necessary and it is possible that the printing apparatus comes to be small and simple. Furthermore, the photo-curing composition which covers a surface of the ink is hard. Accordingly, wear resistance property of the ink comes to be good and the ink is prevented from setting-off.
According to a second aspect of the invention, a hot melt ink which is applicable to an ink jet printing system where the hot melt ink is jetted out to a printing medium to form an image on the printing medium includes: a binder which contains a hot melt composition; a coloring material which is dispersed in the binder; and a photo-curing composition, wherein the binder as a dispersion medium is dispersed in the photo-curing composition in the form of grains and a surface of the hot melt ink is covered with the photo-curing composition before the ink is fixed when the hot melt ink is jetted out to the printing medium.
By the above invention, a flow property of the ink which has jetted out on the printing medium is improved. Accordingly, any fixing process such as process in which heat or pressure is given to the printing medium is not necessary and it is possible that the printing apparatus comes to be small and simple. Furthermore, the photo-curing composition which covers a surface of the ink is hard. Accordingly, wear resistance property of the ink comes to be good and the ink is prevented from setting-off.
In the above invention, a thermoplastic resin may be used as the hot melt composition.
In the above invention, a wax may be used as the hot melt composition.
In the above invention, a diameters of the grain made of the binder may be set within the limits of 1 xcexcm to 30 xcexcm, more preferably, 2 xcexcm to 20 xcexcm.
In the above invention, a wavelength in which the photo-curing composition shows the highest photosensitivity may be within the limits of visible radiation.
According to the third aspect of the invention, an ink jet printing apparatus comprises: a jetting device which jets a hot melt ink melted by heat out to a printing medium to draw an image on the printing medium; and a light source for irradiating the hot melt ink on the printing medium which is jetted out from the jetting device to cure a photo-curing composition included in the hot melt ink, wherein a binder of the hot melt ink as a dispersion medium is dispersed in the photo-curing composition in the form of grains and a surface of the hot melt ink is covered with the photo-curing composition when the hot melt ink is fixed on the printing medium.
By the above invention, the ink jet printing apparatus is provided with a jetting device which for jetting a hot melt ink out to a printing medium to draw an image on the printing medium; and a light source for irradiating the hot melt ink on the printing medium which is jetted out from the jetting device to cure a photo-curing composition included in the hot melt ink. Accordingly, the ink jet printing apparatus can become compact and simple.